Allroad 4.2 won't restart when hot

[audicary]

I have a 2004 Allroad 4.2L Problem I’m having is that after running it at highway speed for a period of time, say an hour or more, if I shut the engine off for s short period of time (say at a rest stop) and then try to restart it, it won’t start until I wait for an unspecified period of time, anywhere from a couple of minutes to 20+ minutes. All the dash lights come on, there’s a slight click but it doesn't crank. I keep trying every minute or so until suddenly, voila, it suddenly starts right up.
I don't have this problem if just driving and stopping around town.

Saw some blogs that pointed to a bad coolant temperature sensor but dealer said not that as even if it was bad the engine might not start but it would at least crank. Is that correct and if so does anyone have any other ideas? This used to happen just periodically but now it happens almost every time.

Thanks

[rollerton]

Nope. That's not it. There are very few sensors that affect the mechanical/electrical ability to start the car, or crank the engine.One of them is the Crank position sensor. When they start to fail they tend to fail more when they're hot. Once it cools off it'll work again. USUALLY you'll get a CEL and error for 'intermittent' failure of that sensor.
If you have a way to check for errors do that first.
Otherwise some other things, like the starter, can fail more when hot. But that's going to take some diagnosis..

[02 A6 2.7T]

...other things, like the starter, can fail more when hot...

^^ My bet is on the starter, based on the symptoms quoted. Should be easier on the V8 vs a 2.7T ...

[mr_dave]

Starter.

[vrmm]

I would clean battery contacts and follow main grounds/power wire. Then pull the starter and open that bad boy up and check it out. Throw it in a growler if you can and test the solenoid. Check the commutator and brushes. Or just get a new one and call it good. After cleaning contacts :)

[kRussia]

Check your coolant temperature sensor. Replace with a new green plug type and try it.

[kRussia]

Check your coolant temperature sensor. Replace with a new green plug type and try it.

Sorry didn't read enough about not cranking. Disregard

[audicary]

Thanks for the reply but curious why the starter would act funky only in those specific situations when the car has been running at speed but never at any other time ?

[vrmm]

Can't say for sure, but perhaps solenoid contacts can't close due to heat.

The brushes, commutator, core/windings and all that seems less likely to be causing the issue. Mayyybe the brushes have had a bad time with the commutator but that makes little sense in this situation. Pretty easy to find out..
Maybe lacquer has degraded and causes a short if expanded.

It's a hard question to guess but if it's a certain speed it may be the frequency of vibrations causing it to heat up^.
Kinda impossible to guess

[JMURiz]

For some reason on my S6 4.2 (timing belt engine) I have found that a hot or warm start has less issues when I turn the ignition key to the 'on' position for a couple of seconds before turning it to start the engine. I'm wondering if it's kind of like an old hot/warm start issue on Porsche 914s where there is kind of a vapor lock due to the engine heat...

Give this a try and it may help.

[A4_n00b]

My bet is that it’s the Crank Reference Sensor.

Mine exhibited the same symptoms before it flat out died. Not an overly costly part but kind of a pain to get to, so I had my indy do it.




-----------------------------------------------
Current: 16 VW Tiguan R-Line 4MO, 15 VW GTI PP, 14 Audi S4

Retired: 12 VW GTI, 10 Audi S4, 08 VWJetta Wolfsburg, 04 Audi allroad 4.2, 04 VW Jetta, 03 Audi A4 3.0

[PaperToast]

^ this, and/or the fuel pump is starting to give up the ghosty
either one can leave you stranded

[glennda5id]

Original Poster says the starter is not starting. You need to diagnose the circuit. The starter needs power and the starter solenoid needs power. Sounds like a starter or wiring issue.

[chris86vw]

fuel pump or CPS would be a crank but doesn't actually catch situation, this seems to be related to the starter or ignition switch like glennda5id is suggesting since OP is saying it doesn't actually crank.

IF it's cranking, for some reason people seem to always say it doesn't crank but it actually is, then CPS would probably be first place to check since that is a common part to work cold but not hot.

[Audibot]

Sounds like the same exact issue going on over here: https://www.audizine.com/forum/showt...6#post13073006

Could be the starter in that case. Might not be making contact anymore when it gets warm.

However, I'd start with the grounding. There's a grounding bar at the battery, and sometimes those bolts corrode, giving you a bad connection. Getting hot and expanding the metal could do that if the bolts are corroded there.

I had a similar one-click and thought it might be the starter motor, and it turned out to be one of the engine grounds by the passenger engine mount had gotten corroded.

[dubzackvr6]

Sounds like a crank position sensor to me.


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[SkiahMutt]

+1 for crank position sensor.

[flyfishing]

ever find out what the prob was?

[Watcher0691]

Thanks for the reply but curious why the starter would act funky only in those specific situations when the car has been running at speed but never at any other time ?

Starter Windings have a short to ground. When you start the car in the morning (or for several hours) everything appears normal. After running for a period of time, you shut off, try and restart, and hear a click!
That is caused by the break in the winding expanding as the engine and engine compartment temperature (heat soak) reaches a point where the current from the battery will take the path of least resistance. Instead of jumping the gap on the broken winding, the current finds a better path with little resistance, starter motor housing!. Don't confuse this with a no-crank condition in which you don't hear a click, with a fully charged battery. That is primarily caused by a bad ground condition. For those old enough to remember, the 1968, 69, 70 Corvette big block motors experienced this same issue until GM engineers figured out that it was a heat issue and put a heat shield over the starter. problem solved!

[flyfishing]

My 2.7 just had this. It was a 10 dollar fix with new battery ground strap.


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[kwaceyoopony]

I had this problem on my 4.2L it ended up being the engine speed sensor


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[audicary]

As an update to my earlier post, I have replaced the starter, the coolant sensor, the battery and fuel pump. The other day doing errands around town on a hot (90+ degrees) and humid day, and after my third stop, each stop consisting of no more than 5-10 minutes driving in between stops of equal length, the problem arose again. it wouldn't start right away, but after trying once every minute or so, it started after 5 or so minutes. Then again after my fourth stop. So it seems like I'm back at square one except it doesn't just take driving at highway speeds for an extended time, it can happen after a limited time of driving in hot and humid weather. Still looking for clues so if anyone has any other ideas on where to look please feel free to suggest

[flyfishing]

check your engine and battery ground strap

[Bordom]

At that point, crank sensor. It's right there on the driver side above the axle approx. The plug is behind coolant expansion tank and the sensor is held in with a 10mm bolt. Takes all of 15mins to change and you wont have hot start issues anymore

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[audicary]

Do you have to remove the coolant expansion tank to get at it ? And is it connected into the firewall? Thanks

[kicker]

So is it the starter that still isnt cranking on occasion when hot?

I had a faulty crank position sensor, it gave a G28 implausible signal DTC and it wouldn't start when hot BUT it would crank non stop without firing if you wanted to. If it is your CPS, with the problem present the rpms will show as zero when cranking, you can watch the tacho but an OBD2 device will be easier as cranking speed is a lot lower than idle.

It sounds like yours is still a heat soak problem but if the starter isn't cranking then you should check that first. Earth strap, wiring, solenoid, starter motor etc

[audicary]

Have replaced the starter, fuel pump, the coolant sensor, and the battery. Supposedly the tech checked the battery straps. Problem only happens when the car has been running awhile at highway speed and then I stop, e.g. at a rest area. All lights in dash come on but car does not crank. After trying occasionally for awhile it starts right up. Never a problem otherwise. My simple mind thinks something either expands when hot to create a break in current to starter, or engine thinks it is over heated and prevents connection as a safety

[Bordom]

Do you have to remove the coolant expansion tank to get at it ? And is it connected into the firewall? Thanks

3 bolts and it swings out of the way

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[audicary]

ok thanks

[Mad Cow]

What kind of starter did you put in? It really sounds like a bad starter and you should never assume the new part you just put in is good. Anecdotal evidence, but I've seen a few brand new supposedly quality brand parts fail soon after installing, a starter being one of them. The starter circuit is really simple, it would still turn over with no ecu whatsoever. If you want to be sure you can check for 12v at the starter solenoid connection when it's refusing to start, but that's easier said than done.